Solid wood moldings, such as those used around doors and windows, are expensive. When it is desirable to have a natural wood finished molding, and it is desired to employ hardwoods such as birch and oak the moldings add significantly to the overall cost of new or remolded buildings. To appear most pleasing, only the highest grade and most costly woods without knots, defects or splices should be employed for the manufacture of wood moldings. Nonetheless, wood moldings manufactured from solid lumber are subject to warping and unpredictable changes in dimension as the moisture content of the molding changes.
To overcome these problems of material costs and dimensional instability, methods have been developed to apply thin wood veneers to substrates composed of low-cost wood particle board, lumber core and the like. Processes and the apparatus to practice them have been developed for wrapping thin veneers of approximately 1/42 inch around three sides of a rectangular substrate. The veneer-wrapped molding is applied around doorways and windows and has a back surface adjacent to a wall which is not fully veneered. In this way, the veneer, which is wrapped around the molding substrate so as to cover all four corners and the front and side faces, but leaving uncovered a portion of the back face, will appear from all visible faces to be constructed of solid wood.
Known methods of profile wrapping moldings include the steps of applying a hot melt glue such as ethylene vinyl acetate (EVA) to one side of a veneer, transporting that veneer by means of transport wheels and adhering the veneer to the substrate.
Two part methods of veneer profile wrapping moldings comprise the method of applying each part of a two part adhesive to the veneer to form a heat resistive coating between the veneer and the substrate.
Other known processes for veneer wrapping employing solvent based glues have been used in which the solvent-based glue is applied to both the veneer and the substrate and where the veneer is wrapped around the board using heat and pressure. Solvent based glues, however, are expensive and the nonaqueous solvent is dangerous to use.
A desirable attribute of veneer profile wrapped moldings is the ability to be used in damp or wet environments. In particular, the molding should be able to pass the American Society of Testing Methods (ASTM) D-3110 Wet Use (Type 1) test. This ASTM test subjects the veneer-wrapped molding to boiling water and vacuum pressure environments to test its ability to survive in a wet use environment. Hot melt glues, which are in widespread use in the industry, soften on exposure to heat and are not sufficiently tolerant to moisture and temperature change to survive this wet use test. Hot melt glues are also subject to a tendency to bleed through the veneer giving a blotchy look if the veneer is stained a dark color. Hot melt glues are also chemically affected by some stains and finishes that will soften the bond between the veneer and the substrate. Machining or routing the veneered substrates produced with hot melt glues reactivates the glue which then becomes gummy and accumulates on cutter or router heads.
Two-part glues have been developed to overcome some of the problems associated with hot melt glues. However, these glues are expensive and are still experimental.
Polyurethane hot melt glues have been developed to be employed in a wet use, but these glues are prohibitively expensive.
Another problem with known methods of profile wrapping substrates is that the veneer used must be quite thin, on the order of 0.024 inches thickness, in order to have sufficient flexibility to be successfully wrapped about the veneer substrate. The thinness of the veneer substrate and known veneer wrapped moldings has detrimental effects on the appearance of the veneer because the thickness limits the amount of finish sanding which may be performed, and hence, the final appearance of the wood grain.
What is needed is a method of veneer profile wrapping substrates which employs a cost-effective, safe, water-base glue system which forms a glue line which is resistant to heat and moisture. Further the method should increase the flexibility of the veneer prior to gluing to allow thicker veneers to be wrapped. There is also a need for a veneer-wrapped molding which can withstand wet use and which has a veneer wrapping which is sufficiently thick to allow finish sanding and an improved veneer appearance.